Hello from The Netherlands

[sito20]

Hello everyone,

I joined this forum to aid me in a research paper I'm writing for school, and because I'm very interested in rocketry.
I'm planning to research the relationship between the radius of the nozzle of a water rocket, and the altitude it reaches in flight. It's still in the early stages, so I'm not 100% set on the independent variable.

As of now, I'm trying to find out if there even is a clear enough relation between the two by testing the effect of different nozzle radii in simulations. And so far, the graph looks more like a seismograph.

Any tips or suggestions will be appreciated, and I look forward to having many great discussions here in the future.

Sito

 

[neil_w]

Welcome! Sounds like a fun project.

 

[smstachwick]

Hello everyone,

I joined this forum to aid me in a research paper I'm writing for school, and because I'm very interested in rocketry.
I'm planning to research the relationship between the radius of the nozzle of a water rocket, and the altitude it reaches in flight. It's still in the early stages, so I'm not 100% set on the independent variable.

As of now, I'm trying to find out if there even is a clear enough relation between the two by testing the effect of different nozzle radii in simulations. And so far, the graph looks more like a seismograph.

Any tips or suggestions will be appreciated, and I look forward to having many great discussions here in the future.

Sito

Altitude is dependent on many, many variables, including ambient weather conditions that are extremely difficult to maintain control over for the duration of the test period. It may be more fruitful for you to focus your research on things you can measure on a static stand, such as the nozzle radius’s effect on thrust duration, thrust at specific points of operation, specific impulse, and/or total impulse.

Nozzle radius isn’t the only parameter you can experiment with, either. The nozzle is a three-dimensional object with a wide variety of geometries possible. With modern 3D printing technology, you should be able to practically build a number of nozzle shapes and static test them at reasonable cost, rotating through various independent variables over the experimental phase.

Even better if there are ways to predict water rocket motor performance mathematically or with computer simulations.

Of course, I don’t know how applicable this will be for water rockets, which don’t have quite the performance potential of model or high-power rockets, but it could be worth looking into.

 

[RocketRev]

Hello Sito,

The shape of the nozzle is every bit as important as the diameter. And are you going with a simple straight cone shape? What degree of cone are you using? Then there are the other shapes like an internal ogive for instance. Lots of shapes available some of which will be more efficient than others.

And if that's not enough, think about the variables concerning the diameter and length of the throat right before you get to the nozzle.

And then there's the shape, length, diameter of the convergence part of the nozzle before you even get to the throat which comes before the nozzle.

Then there's the shape of the transitions between convergence zone, throat, and nozzle? Sharp edge, rounded, or other?

Each of the variables that I mentioned, and I'm certain that I'm missing some, will affect the efficiency of your water rocket's performance. Sounds like a great research project. And I think that Shane in post #3 is absolyutely correct that a 3-d printer and a good test stand would make this project far more fruitful.

Good luck and enjoy!
Brad

 

[Funkworks]

As of now, I'm trying to find out if there even is a clear enough relation between the two by testing the effect of different nozzle radii in simulations. And so far, the graph looks more like a seismograph.

The relation itself, between nozzle diameter and altitude, will depend on parameters defining the rocket, like its weight, water distribution in the tank, drag coefficient, initial speed and possibly other things. I would not expect a simple relation, unless you happen to be in a regime that happens to be somewhat linear. In other words, your results will apply to that rocket alone, and not be generalliy applicable to any rocket. You could call that my hypothesis.
In any case, feel free to prove me wrong, have fun, and

 

[prfesser]

Hello and welcome!

FWIW for a water rocket the exit cone (see De Laval nozzle) is unnecessary. An exit cone helps when the exhaust is a gas, because gases are compressible and will expand past the nozzle throat, creating additional thrust. Water is not significantly compressible, certainly not at the pressures used for water rockets. So a simple hole in the end of the water-motor will suffice.

PM me if you want to reference me as "personal communication" if you like, for any paper you might have to write.

Best -- Terry

 

[OverTheTop]

Welcome to the forum

Have a look at air command water rockets. George is what I call the NASA of water rockets .
http://www.aircommandrockets.com/
He has some great videos on YouTube too.

 

[teepot]

Welcome to the Forum. Hope you find the answers your looking for. Lots of real smart and experienced people here.

 

[sito20]

Altitude is dependent on many, many variables, including ambient weather conditions that are extremely difficult to maintain control over for the duration of the test period. It may be more fruitful for you to focus your research on things you can measure on a static stand, such as the nozzle radius’s effect on thrust duration, thrust at specific points of operation, specific impulse, and/or total impulse.

Nozzle radius isn’t the only parameter you can experiment with, either. The nozzle is a three-dimensional object with a wide variety of geometries possible. With modern 3D printing technology, you should be able to practically build a number of nozzle shapes and static test them at reasonable cost, rotating through various independent variables over the experimental phase.

Even better if there are ways to predict water rocket motor performance mathematically or with computer simulations.

Of course, I don’t know how applicable this will be for water rockets, which don’t have quite the performance potential of model or high-power rockets, but it could be worth looking into.

You're right, the experiment is dependent on too many variables. As well as that, making a good mathematical model is very unrealistic. In an academic paper I read, the mathematical model they created required one to solve 3 simultaneous differential equations. And even then, the model's results differed from the actual experiment by a large amount.

I'm following your advice on performing a static experiment. Measuring thrust and impulse would give the essay a much better focus. I could write a lot more about the different uses and applications of different radii in the discussions section of my essay. And making a mathematical model would be much more feasible.

Thank you for the guidance.

 

[smstachwick]

You're right, the experiment is dependent on too many variables. As well as that, making a good mathematical model is very unrealistic. In an academic paper I read, the mathematical model they created required one to solve 3 simultaneous differential equations. And even then, the model's results differed from the actual experiment by a large amount.

I'm following your advice on performing a static experiment. Measuring thrust and impulse would give the essay a much better focus. I could write a lot more about the different uses and applications of different radii in the discussions section of my essay. And making a mathematical model would be much more feasible.

Thank you for the guidance.

I didn’t expect that to actually be of use, I’m pleasantly surprised that it was. I’d be interested in reading your paper if/when it’s finished.

 

[sito20]

Hello and welcome!

FWIW for a water rocket the exit cone (see De Laval nozzle) is unnecessary. An exit cone helps when the exhaust is a gas, because gases are compressible and will expand past the nozzle throat, creating additional thrust. Water is not significantly compressible, certainly not at the pressures used for water rockets. So a simple hole in the end of the water-motor will suffice.

PM me if you want to reference me as "personal communication" if you like, for any paper you might have to write.

Best -- Terry

Hi Terry,
That's a relief. I was concerned I had to explain that part of thrust in my appendix.
I'll be referencing all this in my documentation. I'm not sure how to private message on here, could you start one with me?

 

[sito20]

I didn’t expect that to actually be of use, I’m pleasantly surprised that it was. I’d be interested in reading your paper if/when it’s finished.

I'll post it on here when it's done

 

[sito20]

The relation itself, between nozzle diameter and altitude, will depend on parameters defining the rocket, like its weight, water distribution in the tank, drag coefficient, initial speed and possibly other things. I would not expect a simple relation, unless you happen to be in a regime that happens to be somewhat linear. In other words, your results will apply to that rocket alone, and not be generalliy applicable to any rocket. You could call that my hypothesis.
In any case, feel free to prove me wrong, have fun, and

Hi Funkworks,
You're right, my previous research question was far too broad and didn't have much resolution. Following the suggestion of smstachwick, I'm conducting a static-fire experiment and likely focus on some properties of thrust during operation while changing the radius.
Though the results will still only really apply to water rockets, I will at least be able to generalize to real rockets and discuss when different thrust profiles are useful.

 

[makoacorde]

Most welcome to join the community!

 

[K'Tesh]

Can't help with the project, but I can say "Hi! And welcome!"

 

[Stewman]

Welcome to the forum! This sounds like an interesting project, wish you success.

 

[Hobie1dog]

Welcome to the forum

 

[Pooklord]

Hello everyone,

I joined this forum to aid me in a research paper I'm writing for school, and because I'm very interested in rocketry.
I'm planning to research the relationship between the radius of the nozzle of a water rocket, and the altitude it reaches in flight. It's still in the early stages, so I'm not 100% set on the independent variable.

As of now, I'm trying to find out if there even is a clear enough relation between the two by testing the effect of different nozzle radii in simulations. And so far, the graph looks more like a seismograph.

Any tips or suggestions will be appreciated, and I look forward to having many great discussions here in the future.

Sito

Welcome to the Forum!